1. Technical Field
The present disclosure relates to a sun tracking method and a sun tracking system. More particularly, the present disclosure relates to a sun tracking method and a sun tracking system that is able to continuously track the position of the sun without additional light sensors, calculation of the solar orbit function, regular calibration of the mechanical structure of the sun tracking system regularly or precise initial installation of the sun tracking system.
2. Description of Related Art
Concentrated photovoltaic (CPV) system is a conventional photovoltaic device that uses optical devices to concentrate a large area of sunlight onto the photovoltaic cells. The method of concentrating the sunlight reduces the area of the photovoltaic cells and makes the CPV system cost-effective. However, it makes the CPV system become sensitive to the incident angle of the sunlight as well. The further reduction of the area of the photovoltaic cells adapted in the highly concentrated photovoltaic system (with a concentration ratio higher than 500) makes the offset of the tracking angle that is tolerable by the light-concentrating module reduced at the same time. Accordingly, the precision of the tracking system becomes more and more important. In order to concentrate the sunlight precisely on the photovoltaic cells, a tracking device is necessary to be adapted to the light-concentrating module to modulate the axis of the light-concentrating module toward the sun.
In the CPV system, the tracking device performs the tracking mechanism in cooperation with the sensing device. The sensing device makes use of a plurality of light sensors disposed in different places and the pillars that o generate shadows to make the light incident to the light sensors uneven. The uneven incident light results in different voltage outputs generated by the light sensors. The direction of the incident light that has the highest intensity can hence be determined by the voltage values of the voltage outputs. There are various kinds of sensors such as optical conductors, photodiodes, phototransistors and photovoltaic cells. Each of the light sensors generates a corresponding short-circuit current according to the intensity of the incident sunlight, where the short-circuit current becomes larger when the intensity of the sunlight becomes higher. The amount of the short-circuit current is then outputted in a voltage form.
Please refer to FIG. 1. FIG. 1 is a 3-D view of a conventional sun tracking system. The conventional sun tracking system is a CPV system having a photovoltaic cell device 11, an attitude control device 12, a light-sensing device 13 and a micro-control device 14. The micro-control device 14 is coupled to the attitude control device 12 and the light-sensing device 13. The attitude control device 12 has an azimuth angle control unit 121 and an elevation angle control unit 122 to adjust the attitude (including an azimuth angle and an elevation angle) of the photovoltaic cell device 11.
When the photovoltaic cell device 11 is in operation, the light-sensing device 13 keeps sensing the intensity of the light incident thereon. The micro-control device 14 drives a motor driving device to drive a motor in the attitude control device 12 according to the light-sensing result to adjust the attitude of the photovoltaic cell device 11 and the light-sensing device 13. However, a time-consuming initial calibration is needed when the light-sensing device is adapted to make the four (or a plurality of) light sensors of the light-sensing device generate the same amount of output voltage/current when the photovoltaic cell device 11 faces directly to the sun.
Moreover, after the conventional sun tracking system operations for a certain time period, the mechanical structure of the system may be damaged, deformed or loosened due to the environmental effect to change the relative position of the photovoltaic cell device 11 and the light-sensing device 13. On the other hand, the light sensors of the light-sensing device 13 deteriorate over time since they are under the sun for a long time. Accordingly, the direction of the incident light having the highest intensity detected by the light-sensing device 13 may not correspond to the attitude of the photovoltaic cell device 11 that can receive the largest amount of sunlight. Comparing to the initial state of the sun tracking system, the efficiency of the conventional sun tracking system degrades more when the operation time is longer.
In order to avoid the above defects, regular calibrations of the mechanical structure are need to make the relative position of photovoltaic cell device 11 and the light-sensing device 13 back to the initial state. However, the regular calibrations make the maintenance cost increase and persecute the maintainer as well.
On the other hand, some conventional sun tracking systems use complex solar orbit function to calculate the position of the sun to adjust the attitude of the photovoltaic cell device. The result of the calculation of the complex solar orbit function is reliable only when the initial position of the sun is extremely precise. If an offset of the initial position is present, the error is generated in the calculation result. Therefore, a precise initial setting of the architecture and the position of the system is unavoidable in such a kind of to conventional sun tracking systems. The installation cost of the conventional sun tracking systems thus increases.
Accordingly, what is needed is a sun tracking method and a sun tracking system that is able to continuously track the position of the sun without additional light sensors, calculation of the solar orbit function, regular calibration of the mechanical structure of the sun tracking system regularly or precise initial installation of the sun tracking system.
Moreover, in order to make the photovoltaic cell device generates the maximum output power, a maximum power point tracking (MPPT) device is installed. The maximum power point tracking (MPPT) device has a voltage-increasing circuit or a voltage-increasing/decreasing circuit. A measurement of the voltage, current or power is performed to generate a feedback signal to control the power transistors of the voltage-increasing circuit or the voltage-increasing/decreasing circuit such that the photovoltaic cell device can always generate the maximum output power after the photovoltaic conversion no matter what the condition of the illumination of the sunlight and the load is. The short-circuit current of the photovoltaic cell or the output power of the photovoltaic cell is also at the maximum value when the photovoltaic cell device faces directly to the sun.